<button (click)="goto('/manager')">管理商品</button>
<button (click)="goto('/shop')">商店</button>
<button (click)="goto('/cart')">购物车
  <ng-container *ngIf="!!carts && carts.length > 0">
    ({{carts.length}})
  </ng-container>
</button>
<br>
<router-outlet></router-outlet>
